PROJECT SUMMARY The development of alcohol use disorders involves a transition to inflexible habitual drug-seeking behavior, resulting in difficulty regulating or terminating drinking behavior. Ethanol exposure is thought to facilitate the expression of habitual ethanol seeking, and indeed our own data indicate that chronic intermittent ethanol exposure (CIE) promotes the expression of this behavior. A growing body of literature suggests that glutamatergic signaling within corticostriatal circuits is dysregulated across chronic ethanol exposure. In particular, data suggest that CIE increases extracellular glutamate in the nucleus accumbens shell (NAcS), and that this effect may be mediated by the loss of presynaptic mGluR2. Despite strong evidence that glutamate signaling within these circuits mediates behavioral flexibility, little is known regarding how NAcS glutamate signaling changes across the development of inflexible reward seeking, and further, how alterations in NAcS glutamate signaling can regulate the expression of actions versus habits. This K99/R00 proposal contains a comprehensive training and research plan based on the applicant?s preliminary findings that regulation of glutamate signaling within the NAcS can reverse CIE-induced deficits in goal-directed behavior, directly implicating NAcS glutamate signaling in response strategy selection. During the mentored portion of the award, the applicant will receive training in cutting-edge laboratory techniques including multielectrode array (MEA) recording in awake behaving mice, pharmacogenetics and optogenetics. The candidate will use this training to test the novel hypothesis that alterations in NAcS glutamate signaling resulting from CIE exposure impair behavioral flexibility. Aim 1 is designed to confirm the hypothesis that CIE-induced deficits in goal-directed ethanol seeking can be reversed by mGluR2/3 agonism and to confirm the neuroanatomical locus of this effect. In Aim 2 we will use MEA recordings to test the hypothesis that acquisition of habitual behavior is accompanied by changes in neuronal activity in the NAcS, as well as synchrony between the NAcS and structures that send glutamatergic projections to this brain region, including the infralimbic prefrontal cortex (IfL), the basolateral amygdala (BLA) and the ventral hippocampus (VH). Aim 3 is designed to test the hypothesis that pharmacogenetic and optogenetic manipulations of activity within distinct glutamatergic projections to the NAcS ? from the IfL, BLA and VH - alter the expression of habitual ethanol seeking. The results of these experiments are expected to provide considerable information on the neurobiology of habitual ethanol seeking and to identify mechanisms through which behavioral flexibility can be restored. We expect that the knowledge gained from these studies will provide significant insight into the development of alcohol use disorders that will ultimately inform the generation of novel prevention and treatment strategies. The training that the candidate receives during the mentored portion of this award is expected to facilitate her career development and transition toward becoming an independent neuroscientist.